Variation in Salmonella typhi Infection Among Local Populations in Southern Benue , Nigeria

© 2018 The Author(s); Published by Alborz University of Medical Sciences. This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background Typhoid fever (enteric fever) is caused by Salmonella typhi which is solely a human pathogen with no known animal reservoir. S. typhi is a gram-negative, motile, rod-shaped and facultative anaerobic bacterium.1 It is a non-spore forming and non-lactose fermenting bacterium. The bacterium is transmitted mainly through consumption of food and water that has been contaminated by faecal matter.2 Clean water, good hygiene and sanitation are factors that prevent the spread of typhoid.1,3,4 The incubation period is usually 1-2 weeks, and the duration of the illness is about 3-4 weeks. Symptoms include poor appetite, headaches, generalized aches and pains, fatigue, weakness, fever as high as 103o to 104oF (39°C to 40°C), lethargy, diarrhoea and rose coloured spot.5,6 Salmonella typhi infection begins with colonization of the small intestine, which progresses to the invasion of the gastrointestinal mucosa. The infection then spreads to the liver, spleen, and bone marrow.1,7 The severity of the infection depends on the initial infective dose, virulence and the host’s immune response.8-10 The greatest burden of disease is experienced by infants, children and adolescents (the World Health Organization [WHO]11 and Crump and Mintz12). In view of the above, the WHO recognizes this disease as a major public health problem and recommends immunization with Vi polysaccharide vaccine in high-risk areas.13 Typhoid fever is an endemic disease in tropical and subtropical climates and has become a major public health problem in developing countries, with an estimated annual incidence of 540 cases per 100 000 people, and an estimated 17 million cases worldwide.11,14 It is often encountered in tropical countries including Nigeria where it constitutes a serious source of morbidity and mortality.15,16 This stems from poor hygienic environment and inadequate water supply systems which have become

major setbacks in the health systems of Asian, and African countries such as Nigeria. 3,17In 2004, Crump et al 18 estimated that typhoid fever caused 21.6 million illnesses globally with 216, 510 deaths in the year 2000 alone.Typhoid fever was estimated to have medium incidence in Africa with 10-100 cases per 100 000 persons. 18However, a recent report has indicated incidence rates higher than 100 cases per 100 000 persons in Burkina Faso, Ghana, Tanzania and Kenya. 19 recent study in Nigeria by Akinyemi et al 20 based on blood culture from Widal positive patients between 1993 and 2017, revealed positivity rates of 7% to 18.6% in Lagos, 3.9% to 10.4% in Kano and 0.8% to 2.4% in Abuja.A slight increase in incidence was observed between 2015 and 2017 in Abuja.20 The incidence of typhoid fever in many parts of Nigeria is not very well known.This has been made difficult by the absence of efficient epidemiological surveillance, coupled with poor or non-existent database of infectious diseases.20,21 Other contributory factors attributed to the spread of typhoid fever in Nigeria include the absence of adequate human waste processing facilities, abuse of antibiotics, lack of portable drinking water, increase in movement of people and inefficient healthcare delivery systems.20 Moreover, it is not uncommon to find patients presenting themselves only after patronizing unapproved treatment outlets.21 The aim of this study, therefore, was to investigate the prevalence of Salmonella typhi in patients attending secondary health centers within the 9 local government areas (LGAs) of Benue and the influence of factors such as season, sex and age of patients in the study area.

Study Area
The study was conducted in Benue.The area lies within the Guinea savannah region of Central Nigeria (Mid-belt region) and experiences a tropical climate with moderate rainfall estimated to average 1173 mm.The rainy season is experienced from April to October while the dry season runs from November to March. 22It has a population of about 1 307 647. 23Benue has 9 LGAs which are Ado, Agatu, Apa, Obi, Ogbadibo, Ohimini, Oju, Okpokwu and Otukpo.

Study Population
The study was hospital-based and was carried out among patients diagnosed with typhoid fever using Widal reaction.The purpose and procedure of the study were explained to the patients (in and out-patients) and demographic information was obtained from each patient through a structured questionnaire.

Sample Collection
A total of 1022 stool samples were collected from patients in Benue State Secondary Health centers within the 9 LGAs of Benue and transported to the Microbiology laboratory of Federal University of Agriculture Makurdi for examination.Samples were collected between August 2016 and July 2017 at various health centers.

Isolation of Salmonella typhi
Each sample was first inoculated into Selenite broth base (Oxoid, CM 0395) and incubated for 18-24 hours at 37 o C for pre-enrichment.Loopfuls of the broth were then streaked onto Salmonella Shigella agar (Oxoid, CM 0099) and Xylose Lysine Deoxycholate agar (Oxoid, CM 0469).Inoculated plates were incubated at 37 o C for 24 hours; suspected colonies were sub-cultured onto Bismuth Sulfite agar (Oxoid, CM 0201) to obtain pure cultures.

Identification of the Isolates
Colonies were identified using their morphological and biochemical characteristics. 24The shape, color and elevation of the bacterial colony were observed visually.Gram reaction, motility, catalase, indole, oxidase, citrate utilization and Triple sugar iron tests were carried out as described by Ochei and Kolhatkar 25 and Arora and Arora. 26ta Analysis IBM SPSS Statistics version 21.0 (IBM Corp., Armonk, NY, USA) was used to analyze the results obtained.Pearson's chi-square test was used to determine the significance of associations between variables.The strength of the association between infection outcome and controlling variables (age, sex and season) was estimated by crude odds ratio using univariate logistic regression, while multivariate logistic regression model was used to compute adjusted odds ratio with 95% CIs.A P value less than 0.05 was considered statistically significant.
The seasonal isolation rate of S. typhi among patients with suspected typhoid was also determined (Table 3).Table 4 shows the variation in isolation with respect to seasons.High isolation rates were recorded between January, 50.0%(31/62) and May, 61.8% (76/123).November accounted for the least rate of isolation, 17.9% (22/123).There was a significant difference in the prevalence rate of S. typhi in relation to the month of sample collection (χ 2 = 94.090,df = 11, P < 0.05).
The relationship of sex, age and season of sample collection with S. typhi infection in patients was also assessed.After adjusting for age, sex and season, males were significantly more prone to get infected (adjusted odds ratio [AOR] = 1.321,CI = 1.027-1.700)than females.Age did not show any significant relationship with S. typhi infection (AOR = 0.993, CI = 0.984-1.022).Although the relationship was not significant, S. typhi infection was more associated with the rainy season (AOR = 1.223,CI = 0.951-1.572)than the dry season.

Discussion
The findings of this study revealed an isolation rate of 43.7% (447/1022) for S. typhi in the study area.This is consistent with those of Mohammed et al 3 and Adabara et al 27 in studies conducted in Nasarawa and Minna in Nasarawa and Niger states, Nigeria respectively.A much higher prevalence was reported by Ifeanyi et al, 16 Kalu et al 28 and Bhatta et al 29 in Abuja and Owerri in Nigeria, and Nepal in Asia, respectively.These findings are in agreement with the position of the WHO 11 that the vast majority of typhoid fever cases occur in Asia, Africa and Latin America where water-borne diseases are highly prevalent.The difference in the isolation rates recorded in various study sites is significant (P<0.05).The high isolation rate recorded in Oju LGA could be attributable to the absence of portable water sources as observed in the LGA.The inhabitants of Ado LGA have access to boreholes in the communities which could explain the low rate of isolation of S. typhi.The rates of S. typhi, including that of the present study, suggest the existence of a significant public health hazard in developing environments.
The difference in the prevalence rate of S. typhi within the age groups is significant (P < 0.05).This corroborates earlier reports by Adabara et al 27 in Minna, Umeh and Agbulu 30 in Makurdi, Central Nigeria, Nigeria and Pato-Mesola et al 31 in Cebu City, India, though a much higher prevalence was reported.The highest prevalence (52.7%) was observed among patients aged ≤10 years old in the present findings, however, it differs from an earlier study by Akter et al 32  are problems.This is because of their level of ignorance which accounts for their quest or desire to satisfy their thirst irrespective of the water source, especially if the water appears to be clean and without color.Their intellectual and mental capability is also not developed enough to maintain required level of hygiene.The high isolation rate recorded in the age group of 51-60 years could be attributable to suppression in their immune system as they grow old. 30The age group of young adults equally recorded a high isolation rate.The possible causes for enteric fever being common in this age group include the high rate of mobility from one place to another, as well as consumption of poorly prepared or unhygienic food and water in schools and colleges. 12The implication of this is that the education of the youth which form the workforce of the zone, as well as farming activities which is the main source of economic livelihood, will be affected and its attendant consequences like illiteracy, economic misfortune and hunger will be great.According to the WHO 11 and Crump and Mintz, 12 the burden of typhoid fever is highest in infants, children and young adults.Health education will play an important role in this age group as illiteracy and low educational status is associated with ignorance, poverty and poor personal hygiene. 33,34almonella typhi isolation rate showed male preponderance over females, suggesting a higher likelihood for men to get infected with S. typhi.This is consistent with earlier findings in different Nigerian cities 16,17,30,[35][36][37] and India. 38The findings of Abd-Alhafeez and Nafi 6 in Khartoum, Sudan, Cinthujah et al 39 in India and Hayat et al 40 in Pakistan also corroborate this finding.This could be as a result of the cultural orientation of the study area.A male is more likely to report to the hospital, and also likely to contract infection due to engagement in more outdoor activities.It is opined that males usually work outside their homes and may eat hawked foods that are liable to contamination and these habits predispose them to infection. 1,30,33Additionally, male folks in the study area engage in farming activities away from their abode, which could occasion the consumption of water from contaminated sources.
The majority of the culture-positive stool samples from suspected typhoid patients in this study were obtained in the early raining season.The highest number of S. typhi was isolated from February to May.This period marks the tail end of the dry season and the onset of raining season in the study area.The result also reveals a significant variation in the isolation rate of S. typhi within the months of January to December (P < 0.05).These findings are consistent with those of Adesina et al, 35 Sudeepa et al, 38 Simental and Martinez 41 and Kumar et al. 42 The low rate of S. typhi isolation recorded during the dry season could be attributable to the fact that the inhabitants abandon the use of streams, rivers and wells because they get dried up, in pursuance of treated water sold in sachets and bottles by water producing companies.This treated water often contains less contaminants than their hitherto source of water.When the rains set in again, locals return to the use of wells, streams and rivers which could have been contaminated by various unhygienic practices.Umeh and Agbulu 30 and Okome-Nkoumou et al 43 opined that typhoid fevers are associated with poor environmental and living conditions, especially in economically poor countries.Most communities in the study area lack treated pipe-borne water, toilet facilities and effective waste disposal systems.They get their drinking water from streams, wells and rivers.Unfortunately, they defecate in nearby bushes and indiscriminately dispose domestic wastes in the environment, at sites which, in some cases, are very close to the same streams and rivers that provide water for the communities.The inhabitants in some of these communities equally bathe in the same body of water used for domestic purposes.It is likely that contamination of food materials or drinking water could be as a result of washed-off faecal matter from the environment, debris and littered garbage during early raining season, which runs into streams and wells used as domestic sources of water.These factors could actually increase the risk of person-to-person spread, especially in the communities.Enteric fever cases occurring throughout the year in this study implies a large number of carriers could be present in the society.Provision of potable water and healthcare facilities by authorities at various levels is required in order to put a break to the endemic nature of the infection.To limit the spread of faecal-orally transmitted infections, enlightenment programs on basic rules of hygiene for communities should be encouraged.Disinfection of drinking water either by boiling, chlorination or addition of sodium aluminate (alum) should be encouraged.Although all patients tested positive for S. typhi when Widal test was used, culture method, however, revealed otherwise.This finding further proves that Widal test as a method for diagnosis of typhoid fever in patients may not be as sensitive as the use of culture, which has remained the gold standard test.The use of Widal test could lead to overestimation of typhoid incidence among a population. 19Unfortunately, most health centers in rural areas within Nigeria lack appropriate materials for diagnosis using culture method, due to its expensive and time-consuming nature.It has, however, been opined that culture method may show negative result especially when the patient has previously used antibiotics. 6It is thus, imperative for health centers in Nigeria to adopt the use of more sensitive and specific rapid detection methods such as Typhidot-EIA test and dot ELISA for diagnosis of typhoid fever.

Conclusion
The present study shows a high incidence of typhoid (43.5%) in Southern Benue.Although all 1022 patients were diagnosed with typhoid fever using the Widal test, only 447 samples were positive using culture method.Hence, a review of the approach to the diagnosis of typhoid fever in the study area is advocated.Moreover, public enlightenment on good personal and environmental hygiene practices could help reduce the spread of the disease among inhabitants of the area.

Table 1 .
in Dhaka City Bangladesh, where the highest prevalence rate was observed in the age group 21 to 30 years.Individuals older than 60 years of age showed a much lower prevalence rate.It is reasoned that children form the most vulnerable group in environments where inadequate water supply and poor environmental hygiene Isolation Rates of Salmonella Typhi in Benue

Table 3 .
Seasonal Isolation Rate of Salmonella typhi Among Typhoid Fever Patients

Table 4 .
Association of Risk Factors With Salmonella typhi Infection a P < 0.05.